The present invention relates to a process and composition for improved mutual compatibility of olefin-based polymers and polar polymers having nitrogen functionality, in oil.
A variety of polymeric and oligomeric additives are sometimes added to lubricating oil compositions and concentrates in order to improve the performance properties of the oil. One class of such compounds is olefin-based polymers, which are often used as viscosity modifiers. Another class of such compounds is polar, nitrogen-containing polymers, which likewise are often used as viscosity modifiers, and which further can be used to impart dispersant performance to an additive packages. Materials from each of these classes normally exhibit a reasonable degree of solubility in oil or in similar hydrocarbon solvents. That is to say, individually members of each class of compound can normally be dissolved in oil in a sufficient quantity to provide a concentrate for later dilution to prepare a fully formulated lubricant.
However, it is often observed that these classes of additives cannot be satisfactorily used together, particularly in a concentrate. For reasons which are not fully understood, concentrates which contain both oil-soluble, olefin-based polymers and oil-soluble polar polymers having nitrogen functionality often undergo a physical or chemical interaction which leads to incompatibility between the species as evidenced by phase separation. Phase separation, as used in this application, is to be interpreted broadly and can be evidenced by the development of haziness upon mixing of two otherwise transparent solutions or by the failure of a mixture of polymers of the two types to form a clear solution when mixed in oil. In severe cases the phase separation can be evidenced by the gross physical separation of the mixture into two or more phases of liquids, solids, or semisolids.
Such phase separation is almost always undesirable. Concentrates which exhibit severe phase separation may require stirring or heating in order to restore gross uniformity and to permit the concentrate to be effectively used. Even minor instances of phase separation are undesirable to the extent that they detract from the appearance and marketability of the concentrates. This incompatibility is most often a problem at temperatures of -18.degree. to +65.degree. C., which represents in many cases the range of temperatures at which concentrates of such additives are shipped or stored. The present invention provides a way to avoid such problems of incompatibility among otherwise oil-soluble polymeric additives.
U.S. Pat. No. 4,594,378, Tipton, Jun. 10, 1986, discloses a mixture of an oil-soluble polymer which is a homopolymer of a non-aromatic monoolefin or a copolymer thereof with an aromatic monoolefin, a nitrogen-containing ester of a carboxyl-containing interpolymer, and a viscosity-reducing liquid organic diluent such as a naphthenic oil or an alkylated aromatic material. Examples of such oils include benzenes substituted with hydrocarbon-based groups of about 8 to about 30 carbon atoms.
U.S. Pat. No. 4,546,137, Rossi et al., Oct. 8, 1985, discloses an additive combination for improving the cold flow properties of distillate fuels, comprising (a) an ethylene containing polymer, e.g. a copolymer of ethylene with vinyl acetate, (b) a hydrocarbon polymer, e.g. copolymers of ethylene and propylene or hydrocarbon polymers derivatised to contain polar groups (e.g. by grafting onto them maleic anhydride followed by amination), and (c) a polar oil soluble compound, which includes amides, salts, carboxylates, sulfonates, sulfates, phosphates, phenates, and borates, having hydrocarbon solubilizing groups; nitrogen compounds are particularly effective as component (c).